Cryptococcal Antigen Latex Agglutination System (CALAS®)

Newly emerging disease states and therapies have been shown to increase the
opportunity for nonspecific interference in some serum specimens. Pretreatment of
serum specimens with pronase prior to utilization of the CALAS kit reduces nonspecific
interference and enhances the detection of capsular polysaccharide antigens of
Cryptococcus neoformans.
PRINCIPLE OF THE TEST
CALAS utilizes latex particles coated with anti-cryptococcal globulin (Detection
Latex). The Detection Latex reacts with the cryptococcal polysaccharide antigen
causing a visible agglutination. Latex particles coated with normal globulin (Control
Latex) act as one of the control reagents. Nonspecific agglutination may occur due to
the presence of certain macroglobulins (e.g. rheumatoid factors) in patient specimens.
Treatment of serum specimens with pronase (Meridian Bioscience, Inc. Catalogue
#140050) removes rheumatoid factor and other nonspecific interference. 12 These
macroglobulins can be demonstrated in serum from patients with rheumatoid arthritis,
sarcoidosis, cirrhosis, syphilis, scleroderma, psoriasis, gout, systemic lupus
erythematosus and other conditions. 1,11 Nonspecific interference is detected by the
Control Latex reagent.
Agglutination of both the Control Latex and the Detection Latex requires two-fold
serial titration of the specimen with both reagents. A four-fold higher titer with the
Detection Latex than with the Control Latex is suggestive of cryptococcal disease but
requires follow-up with specimens collected later in the course of the disease and
culture results. 10 Titers with less than four-fold differences are considered equivocal
test results and further follow-up is recommended (see INTERPRETATION OF
RESULTS).
2